| Exploitation of heterosis is one of the major example of genetics that could increase the yield of crops, save the land, have made the significant contribution to the world. The genetic basis of heterosis has been discussed for nearly a century. The dominance hypothesis attributes the greater yield of hybrids to the suppression of deleterious recessive from one parent by dominant alleles from the other. The overdominance hypothesis assumes that at the key loci the heterozygote is superior to either homozygote (Bruce, 1910; Shull, 1908; Jones, 1917) .The progress of the biotechnology provides the opportunity to elucidate the mechanism of heterosis in genome level. Stuber et al. (1992) considered the overdominance is the major genetic basis of heterosis in maize; Xiao et al. (1995) suggested the dominance is the major molecular mechanism of heterosis in rice. Subsequently, Yu et al. (1997) and Hua et al. (2003) demonstrated the epistasis made the siginificant contribution to heterosis in rice. The aforementioned studies continued the discussion of the genetic basis of heterosis since the 20th century, and little consensus has emerged.Although all the genes in hybrid are derived from its parental inbreds, hybrid performance is quite different from its parental inbreds. Therefore, differential gene expression between hybrids and their parents should be also responsible for the observed heterosis (Sun et al., 1998). Hu et al.(1999) and Sun et al.(1999) respectively probed into the relationship between gene expression and heterosis, they both advanced there were close relationship between gene differential expression and crop heterosis. Along with the emergence of DNA microarray, it is likely to provide new avenues for studying intractable, complex traits, such as heterosis. Such broad-based views of genome-wide gene expression patterns could decipher the mathematic change of gene expression and explain the spatio-temporal patterns of gene expression (Kehoe et al., 1999) .Huayouza6, a new semi-winter Brassica napus variety with high-yield, good quality, prematurity and extensive adaptability, was derived from the cross between the female parent 8086A and male parent 7-5. In the regional trial of the middle and lower reach of Yangtze River in china, Huayouza6 yielded 2175.8kg ha-1 averagely in 2000-2002, 15.52% higher than the control variety Zhongyou 821. Eruic acid, glucosinolates and oil contents of Huayouza6 were 0.4%, 27.78μmol/g, 40.4%, respectively. It was registered and released in 2002-2004 in Hubei province, Anhwei province, Hunan province, china, and Henan province. Two cDNA-based Arabidopisis microarray were used to analyze gene differential expression in cotyledon, 7-leaves seedling, buds of an elite B.napus hybrid Huayouza6 and its parents, in order to elucidate primarily the molecular mechanism of heterosis in Brassica napus. The main results are as follows:In the cotyledon, there were 45 over-expression transcripts and 73 under-expression transcripts between Huayouza6 and its female parent 8086A, in total 118 transcripts, accounting for 5.12% of the total genes in the microarray. On the other hand, there were 105 over-expression transcripts and 126 under-expression transcripts between Huayouza6 and its female parent 7-5, in total 231 transcripts, accounting for 10.03%. In addition, the...
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